Randomised national land management pathways for net-zero emissions: An Irish case study

Global scenario modelling to achieve “net-zero” emissions lacks national resolution, especially in the agriculture, forestry and other land use (AFOLU) sector. This makes effective climate policymaking extremely difficult. Using Ireland as a case study, we have assessed 850 randomized scenarios of activity combinations for Ireland’s AFOLU sector in the year 2050 and evaluated associated greenhouse gas fluxes to the year 2100, using a GWP100 net-zero greenhouse gas definition.
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As the world experiences unprecedented drought conditions, the pressing need to find feasible pathways to “net-zero” emissions is emphatically underscored. The Intergovernmental Panel on Climate Change has made clear that stabilisation of the climate will require, at least, the achievement of net-zero CO2 emissions and strong and sustained reductions in CH4 emissions. Modelling for global climate stabilisation scenarios lacks national level resolution, particularly for the agriculture, forestry, and other land use (AFOLU) sector. Higher resolution scenario modelling is urgently needed to inform effective climate action by governments, companies and individuals. Ireland provides a unique case study opportunity given the juxtaposition between expansion of a profitable and comparatively, efficient agri-food sector and increasingly pressing climate targets

Ireland’s agriculture sector accounts for 34% of the national GHG emissions profile, with the vast majority originating from milk and beef production. Further, around 9 million tonnes CO2 eq. per annum are emitted from drained grasslands on organic soils. Given that CO2 removals from the atmosphere into mineral soils under grass and forests amount to between 2 and 5 million tonnes of CO2 eq. annually, Ireland’s land use land use change and forestry (LULUCF) sector is a net emitter (circa 4 million tonnes CO2 eq. per annum), even before agriculture is considered. In terms of ambition, Ireland’s climate action plan sets a 51% reduction target for national emissions by 2030. Given the contribution of the AFOLU sector to national emissions, and the potential contribution of the sector in terms of removals, generation of feasible scenarios that can illustrate the scale of land use change necessary to achieve looming targets are urgently needed.  

Most modelling to date has looked at modest emission mitigation achievable through abatement options in the agriculture sector, with limited land use change. Extrapolations of past trends, even with additional abatement, will never meet net-zero emission targets, and discussion of more substantial land use change is often curtailed by socio-cultural and political sensibilities. In this context, our goal was to take a back-casting approach and randomly generate (850) scenarios of land use activity combinations in the Irish AFOLU sector to the year 2050 in order to see which AFOLU configurations could be compatible with net-zero emissions, from 2050 out to 2100. To do this we used the new biophysical GOBLIN (General Overview for a Back-casting approach of Livestock Intensification) model, integrating randomly varied input parameters to determine net GHG fluxes across the entire AFOLU sector. The particular value of this goal-oriented, forward-looking approach is that it circumnavigates preconceptions and perceived barriers to land use change encountered when co-constructing scenarios with stakeholders. Illustrating the magnitude of change required to achieve net-zero, and real trade-offs across sub-sectors, is a critical first step to guide stakeholders beyond the marginal abatement thinking that has dominated hitherto - and towards the zero-sum game of net-zero emissions that requires transformative change. Meanwhile, the randomised nature of scenario development in GOBLIN minimises the risk of model designer- and/or user-bias in seeking prospective net-zero solutions (of which there are many permutations).    

We categorised random scenarios based on their net fluxes, as: (i) N-Z-Fail (greater than 2.5 million tonnes CO2 eq. annually); (ii) N-Z-AFOLU (between plus or minus 2.5 million tonnes CO2 eq. annually); (iii) N-Z-National (less than minus 2.5 million tonnes CO2 eq. annually). The latter categorisation represents a 5-10% offset of current non-AFOLU sector emissions, as likely to be needed to achieve national climate neutrality.  

Of the 850 scenarios tested, 666 were categorised as N-Z-Fail, while 146 and 38 scenarios were categorised as N-Z-AFOLU and N-Z-National, respectively. Achieving net-zero by 2050 required a significant reduction in national herd numbers, with average reductions of 42-52% for dairy and 38-44% for beef herds for  N-Z-AFOLU and N-Z-National scenarios, respectively. Herd reductions, spare a considerable area of land. However, alone, they do not come close to achieving net-zero. Active management of a large portion of this spared land for carbon dioxide removal (CDR) is critical to achieve net-zero. In fact, scenarios with higher proportions of spared land actively managed for CDR required smaller herd reductions to achieve net-zero compared to other scenarios with lower proportions of land managed for CDR.

Average values for herd reduction, annual afforestation rates (to 2050) and proportion of total available drained organic grassland area rewetted.

Figure1. Average values for herd reduction, annual afforestation rates (to 2050)

and proportion of total available drained organic grassland area rewetted.

Icon credits: Freepik (www.flaticon.com)

High rates of afforestation proved to be essential to achieve net-zero. The average annual afforestation rates associated with N-Z-AFOLU and N-Z-National were 36 and 46 kha, respectively, to 2050 (see Fig.1 for details of average herd reduction, annual afforestation rates and rewetted area related to N-Z-AFOLU and N-Z-National). Ireland’s forest landscape is dominated by the coniferous species, Sitka Spruce. Afforestation in the scenarios achieving neutrality was typically split quite evenly between broadleaf (48% and 45% for N-Z-AFOLU and N-Z-National, respectively) and coniferous species, meaning that, although Sitka Spruce accumulates carbon faster than broadleaf species, forest biodiversity need not be sacrificed to achieve net-zero. However, the rotational nature of commercial forestry means that the forestry sink will dramatically weaken during periods of intense harvesting (see Fig. 2 for average emissions/removals related to N-Z-Fail, N-Z-AFOLU and N-Z-National) – unless afforestation continues beyond 2050 (not considered in our modelling). Thus, current results indicate that achieving net-zero by 2050 could be fleeting, and unlikely to last out to 2100 - only 40 out of the 850 scenarios sustained net-zero within the AFOLU sector, and only one single scenario sustained net-zero at national level. Whilst GOBLIN accounts for carbon storage in the first generation of harvested wood products, which does mitigate the weakening forest sink somewhat, it does not yet incorporate important substitution factors (avoided emissions where concrete, steel or other materials are substituted by wood), nor cascading uses of wood – which have recently been show to dramatically extend the mitigation effect of commercial forestry. Further research is needed to verify whether cascading use of wood in the bioeconomy, potentially culminating in bioeconomy carbon capture & storages (BECCS), could secure long-term climate stabilisation.

CO2 removals from biomass growth and net carbon storage increment in harvested wood products (HWP

Figure 2. CO2 removals from biomass growth and net carbon storage increment in harvested wood products (HWP). Displayed from 1990 through to 2120 (a), and net CO2e emissions and removals to 2050 (b). Removals for the 2015 baseline year are indicated

Overall, it is clear  that whilst there is a stark urgency to achieve net-zero emissions by 2050 in order to stabilise the climate system, we need to look beyond 2050 to ensure that proposed solutions are sustainable, and that net-zero is not just a fleeting result. Whilst many AFOLU configurations could achieve net-zero, they require all of the following: substantial cattle herd reduction, a dramatic increase in rates of afforestation, re-wetting most of the area of drained organic soils. It is the balance of these actions that could vary considerably. For example, less ambition on afforestation or organic soil rewetting out to 2050 would mean larger herd reductions are needed to achieve net-zero. Given this reality, the continued success of Ireland’s agri-food sector could very much depend on a paradigm shift among stakeholder groups, who currently view forest related land use as competition for agricultural land use, rather than a synergistic CDR mechanism that will allow for higher levels of production in face of looming target deadlines. Stakeholders must also be aware that sustainability of net-zero requires reductions that go beyond the bare minimum required to achieve net-zero by 2050. The achievement of net-zero will be a hollow victory if the sacrifices made to get there are rendered inadequate via a lack of ambition. Dealing with difficult circumstances today is far more desirable than becoming a victim of catastrophic circumstances tomorrow. Doing things by half equates to a continued kicking of the proverbial can. 

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